Trends in microelectronic devices are toward increasing miniaturization, circuit density, operating speeds and switching rates. These trends directly impact the complexity associated with the design and manufacture of microelectronic packages, which may include dice, carrier substrates and the like, as well as computing devices in general. Examples of computing devices include, but are not limited to servers, personal computers and “special” purpose computing devices. Personal computers may have form factors, such as desktop, laptop, tablet, and the like. “Special” purpose computing devices may include set top boxes, personal digital assistants, wireless phones, and the like.
In particular, attention has increasingly shifted to microelectronic packaging as a way to help meet the demands for enhanced system performance. As demand increases, it has become necessary to use multiple dice and or microelectronic packages that work in conjunction with one another. When using multiple dice or microelectronic packages, however, it becomes critical to position the dice close together since excessive signal transmission distance may deteriorate signal integrity and propagation times. The use of conventional single-die microelectronic packages, however, is not commensurate with the need to shorten signal transmission distance because they typically have an area (or footprint) many times larger than the area of the die. This not only increases transmission distances, but it also decreases packaging density.
One solution to create higher density packaging, reduce area requirements and shorten signal transmission distances has been to vertically stack microelectronic packages, such as ball grid arrays (BGA) and chip scale packages (CSP), in an array. Although these stacked microelectronic packages provide certain advantages, further size reduction and performance enhancement has been difficult to obtain due to the physical dimension, design and manufacturing constraints of the individual microelectronic packages and the interconnection to the other microelectronic packages in the array.
A number of problems exist with stacking microelectronic packages. One problem, for example, is that carrier substrates may warp or flex during manufacturing or under certain operating conditions due to factors such as heat, pressure and weight. Flexing and sag are undesirable because it can result in open connections and reduce solder ball co-planarity, which makes it more difficult to couple microelectronic packages together, electrically and mechanically. These problems can result in microelectronic package failure or significantly reduce effectiveness and performance.